23,528 research outputs found
A new cosmic microwave background constraint to primordial gravitational waves
Primordial gravitational waves (GWs) with frequencies > 10^{-15} Hz
contribute to the radiation density of the Universe at the time of decoupling
of the cosmic microwave background (CMB). The effects of this GW background on
the CMB and matter power spectra are identical to those due to massless
neutrinos, unless the initial density-perturbation amplitude for the
gravitational-wave gas is non-adiabatic, as may occur if such GWs are produced
during inflation or some post-inflation phase transition. In either case,
current observations provide a constraint to the GW amplitude that competes
with that from big-bang nucleosynthesis (BBN), although it extends to much
lower frequencies (~10^{-15} Hz rather than the ~10^{-10} Hz lower limit from
BBN): at 95% confidence-level, Omega_gw h^2 < 6.9 x 10^{-6} for homogeneous
(i.e., non-adiabatic) initial conditions. Future CMB experiments, like Planck
and CMBPol, should allow sensitivities to Omega_gw h^2 < 1.4 x 10^{-6} and
Omega_gw h^2 < 5 x 10^{-7}, respectively.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Let
Automatic Generation of Matrix Element Derivatives for Tight Binding Models
Tight binding (TB) models are one approach to the quantum mechanical many
particle problem. An important role in TB models is played by hopping and
overlap matrix elements between the orbitals on two atoms, which of course
depend on the relative positions of the atoms involved. This dependence can be
expressed with the help of Slater-Koster parameters, which are usually taken
from tables. Recently, a way to generate these tables automatically was
published. If TB approaches are applied to simulations of the dynamics of a
system, also derivatives of matrix elements can appear. In this work we give
general expressions for first and second derivatives of such matrix elements.
Implemented in a computer program they obviate the need to type all the
required derivatives of all occuring matrix elements by hand.Comment: 11 pages, 2 figure
Localization of Two-Component Bose-Einstein Condensates in Optical Lattices
We reveal underlying principles of nonlinear localization of a two-component
Bose-Einstein condensate loaded into a one-dimensional optical lattice. Our
theory shows that spin-dependent optical lattices can be used to manipulate
both the type and magnitude of nonlinear interaction between the ultracold
atomic species and to observe nontrivial two-componentnlocalized states of a
condensate in both bands and gaps of the matter-wave band-gap structure.Comment: 4 pages, 4 figure
Selection of imprinted nanoparticles by affinity chromatography
Soluble molecularly imprinted nanoparticles were synthesised via iniferter
initiated polymerisation and separated by size via gel permeation
chromatography. Subsequent fractionation of these particles by affinity
chromatography allowed the separation of high affinity fractions from the
mixture of nanoparticles. Fractions selected this way possess affinity similar
to that of natural antibodies (Kd 6.6 × 10−8) M and were also able to
discriminate between related functional analogues of the templ
Analysis of navigation pattern in the sport of rowing
The effect of weather and environmental conditions on sports has been extensively studied over the last few years (Pezzoli et al., 2010). Based upon the studies of Lobozewicz (1981) and of Kay and Vamplew (2002), Pezzoli and Cristofori (2008) have studied the impact of some specific environmental parameters over different sports using a particular impact index divided into five classes. This analysis clearly shows that most of the outdoor sport activities are strongly influenced by the variation of meteorological parameters. However the impact of meteorological conditions on outdoor sport activities has not yet been extensively studied. The aim of this research is to show that an accurate assessment of wind and wave parameters enables decisive improvements in both training and race strategy planning. Furthermore this analysis provide a very innovative working method for the applied sport research. The work has been based on in-situ measurements of both environmental and performance parameters (wind direction, wind velocity, boat speed and stroke rate) made over different classes and in different race conditions during the 2009 FISA World Championship (Poznan, Poland). In particular a detailed environmental analysis was performed by measuring the wind direction, the wind speed and by evaluating the significant wave height and the wave peak period for each class during the semi-final phase and the final phase. It should be noted that, since wind is a key parameter affecting not only the boat speed but also the race strategy, the assessment of the wind velocity and of the wind direction has been made in connection with the boat movement. The comparison between coupled wind-wave data, boat speed and stroke rate evidently demonstrates that only crews that managed the adaption to changing in the environmental conditions from semi-final to final phase of the race, were able to get better results. References Kay, J., & Vamplew, W. (2002) Weather beaten: sport in the British climate. London: Ed. Mainstream Publishing. Lobozewicz, T. (1981) Meteorology in sport. Frankfurt: Ed. Sportverlag. Pezzoli, A,, Moncalero, M., Boscolo, A., Cristofori, E., Giacometto, F., Gastaldi, S., & Vercelli, G. (2010) The meteo-hydrological analysis and the sport performance: which are the connections? The case of the XXI Winter Olympic Games, Vancouver 2010, Journal of Sports Medicine and Physical Fitness, 50: 19-20. Pezzoli, A., & Cristofori, E. (2008) Analisi, previsioni e misure meteorologiche applicate agli sport equestri, in: 10th Congress "New findings in equine practices, Druento: Centro Internazionale del Cavallo Ed., p.38-4
The stabilisation of receptor structure in low cross-linked MIPs by an immobilised template
In molecularly imprinted polymers (MIPs) a high level of cross-linking is
usually important for preserving the receptor structure. We propose here an
alternative approach for stabilising binding sites, which involves the use of an
immobilised template. The idea is based on the assumption that an immobilised
template will ‘‘hold’’ polymeric chains and complementary functionalities
together, preventing the collapsing of the binding sites. To test this
postulate, a range of polymers was prepared using polymerisable (2,4-diamino-6-
(methacryloyloxy)ethyl-1,3,5-triazine) and non-polymerisable (or extractable)
(2,4-diamino-6-methyl-1,3,5-triazine) templates, methacrylic acid as functional
monomer and ethylene glycol dimethacrylate as cross-linker. The level of cross-
linking was varied from 12 to 80%. Polymerisations were performed in
acetonitrile using UV initiation. Binding properties of the synthesised
materials were characterised both by HPLC and equilibrium batch binding
experiments followed by HPLC-MS or UV-visible detection. The adsorption
isotherms of polymers were obtained and fitted to the Langmuir model to
calculate dissociation constant, Kd, and concentration of binding sites for each
material. The results strongly indicate that the presence of an immobilised
template improves the affinity of MIPs containing low percentages of cross-
linker. The low cross-linked MIPs synthesised with a polymerisable template also
retain a reasonable degree of selectivity. Low crosslinked MIPs with such
binding characteristics would be useful for the creation of new types of optical
and electrochemical sensors, where induced fit or the ‘‘gate effect’’ could be
used more effectively for generating and enhancin
Tidally Induced Offset Disks in Magellanic Spiral Galaxies
Magellanic spiral galaxies are a class of one-armed systems that often
exhibit an offset stellar bar, and are rarely found around massive spiral
galaxies. Using a set of N-body and hydrodynamic simulations we consider a
dwarf-dwarf galaxy interaction as the driving mechanism for the formation of
this peculiar class of systems. We investigate here the relation between the
dynamical, stellar and gaseous disk center and the bar. In all our simulations
the bar center always coincides with the dynamical center, while the stellar
disk becomes highly asymmetric during the encounter causing the photometric
center of the Magellanic galaxy disk to become mismatched with both the bar and
the dynamical center. The disk asymmetries persist for almost 2 Gyrs, the time
that it takes for the disk to be re-centered with the bar, and well after the
companion has passed. This explains the nature of the offset bar found in many
Magellanic-type galaxies, including the Large Magellanic Cloud (LMC) and NGC
3906. In particular, these results, once applied to the LMC, suggest that the
dynamical center should reside in the bar center instead of the HI center as
previously assumed, pointing to a variation in the current estimate of the
north component of the LMC proper motion.Comment: 12 pages, 8 figures, corrected for referee comment
- …